Sarcoidosis is a systemic granulomatous disease of unknown etiology that likely involves exposure to some environmental agent in a genetically susceptible host. We propose to identify sarcoidosis susceptibility genes and determine how thee genes and environmental risk factors interact to cayuse sarcoidosis. This will be accomplished by organizing a multicenter consortium to recruit an adequate sample of sarcoidosis families for analysis We plan to use affected sibling pair linkage analysis to scan the genome for linked chromosomal regions, transmission disequilibrium testing to evaluate candidate genes in those regions with evidence for linkage and an environmental questionnaire to collect data for possible interactions of susceptibility genes with exogenous risk factors.